Abstract

[Truncated abstract] Background and aims: Salinity impedes agricultural productivity across large areas of the arable land on earth, and much scientific research aims to discover strategies for boosting crop and forage production on saline land. This thesis aims to deepen the scientific understanding of the mitochondrial and respiratory response to salt treatment, and investigate how mitochondrial properties vary between wheat varieties with contrasting salinity tolerance. These results could guide future crop breeding efforts, by identifying specific wheat genes as targets for enhancing salinity tolerance processes. Experimental strategies: Wheat plants were grown under laboratory conditions and subjected to either control or NaCl treatment. The approach used to analyse mitochondrial salinity responses involved integrating data from proteomics, physiology and biochemistry. The proteomic techniques of 2D gels and mass spectrometry were employed to investigate which mitochondrial proteins differed in abundance between control versus stress conditions, and also which mitochondrial proteins differ in abundance between tolerant versus sensitive varieties. Physiological techniques were used to analyse how photosynthetic and respiratory rates responded to NaCl, and biochemical techniques were used to investigate how rates of mitochondrial oxygen consumption differed between mitochondria isolated from control versus salt treated plants. Also, this thesis contains a detailed investigation into how the direct application of NaCl to isolated mitochondria affects oxygen consumption rates across different pathways of mitochondrial electron transport. Key results: The bulk of the data in this thesis uses 2D gels to investigate mitochondrial protein composition and its response to salinity stress across wheat varieties. This provides a descriptive catalogue of the proteins that are targeted to wheat mitochondria, and documents a set of mitochondrial proteins that exhibited differential abundance between varieties and according to salt treatment. The key result of these proteomic studies involves the enzyme manganese superoxide dismutase, which exhibited consistently higher abundance in mitochondria isolated from salt treated plants. Interrogation of 2D gel position and mass spectrometry data derived from manganese superoxide dismutase protein spots shows that certain manganese superoxide dismutase isoforms are correlatively linked to varietal salinity tolerance. This study also identified differential abundance in other mitochondrial proteins between varieties, such as beta-cyanoalanine synthase. I posit that these flexible components of the mitochondrial proteome could contribute toward differing varietal salinity tolerance. The other focus of this thesis involved measuring respiratory rates in plant tissues and isolated mitochondria exposed to NaCl. The results of these analyses showed that NaCl treatment can elicit a diversity of respiratory stimulations and inhibitions, in both whole tissue and isolated mitochondria. Root…